Fig.1 shows the microstructure evolution during thermal exposure at 1200℃ and 1300℃. Before thermal exposure, many inter-lamellar 2D pores indicating the typical feature of limited inter-splat bonding can be clearly observed. However, after 5 h of thermal exposure at 1200 ℃, the number of the inter-lamellar 2D pores decreased significantly. Then, when the exposure duration was extended to 100 h at 1200℃, the lamellar structure feature almost disappeared and many spherical pores appeared in the coating. The microstructure evolution of the coatings during thermal exposure at 1300℃ presented the same tendency as that observed at 1200℃. However, the microstructure changed more rapidly at 1300℃ compared with that changed at 1200℃.Moreover, as the exposure duration was increased, the number of the spherical pores decreased while the size of the spherical pores significantly increased. That was ascribed to the decrease of the surface energy: the free surface of the system tends to decrease during thermal exposure and the specific surface area of the pores with small size is larger than that of the pores with larger size.Therefore, during thermal exposure, the small pores sintered fast while the volume of the pore with larger size may increase for the sintering of the small pores nearby. This phenomenon is more evident for the coating containing nanoscaled pores as reported by Lima et al.
Fig.1. Cross section microstructure of La2Zr2O7 coating before and after thermal exposure at 1200℃ and 1300℃ for different durations:(a) as-sprayed La2Zr2O7 coating.(b)1200℃5h,(c)1200℃ 100h,(d)1300℃ 5h,(e)1300℃20 h,(f)1300℃ 100h.
本文由桑尧热喷涂网收集整理。本站文章未经允许不得转载；如欲转载请注明出处，北京桑尧科技开发有限公司网址：http://www.sunspraying.com/
|
